Odor elimination apparatus for extruded plastic

ABSTRACT

Odor elimination process for plastic film in which at least two extruded plastic films are combined outside of the die. The process utilizes a valve adapting a single extruder to supply two melt streams to a dual melt chamber dual slot die. One melt chamber of the dual slot die is heated to a temperature below the temperature of oxidation of the resin of the thermoplastic material extruded through the die. The other melt chamber is heated above the oxidation temperature of the thermoplastic material extruded through the die, to increase the adhesive qualities of the extruded film to effectively bond with the thermoplastic material heated to a low temperature. The two films are then combined and the high temperature film is sandwiched between the low temperature film and a substrate, trapping the odor of the high temperature film. In a modified form of the invention, the film heated to a high temperature is passed through a tortuous path and heated to its high temperature while passing through this path.

This is a continuation of application Ser. No. 544,218, filed Jan. 27,1975, now abandoned, which is a divisional of application Ser. No.368,958 filed Jan. 11, 1973 now U.S. Pat. No. 3,901,636.

FIELD OF THE INVENTION

Elimination of oxidized resin odor on an outside sheet of extrudedplastic film.

BACKGROUND AND OBJECTS OF THE INVENTION

An article entitled "Extrusion Coating and Adhesive Lamination forPackaging Materials" published in PLASTICS DESIGN AND PROCESSING in theOctober, 1972 issue, recognizes that polyethylene odor is generallyunacceptable for food packaging and the difficulty in reducing thisodor. An article on page 548 of the April 4, 1972 issue of Tappidiscloses a dual slot die for heating plastic materials to differenttemperatures and discusses controls for the melt temperatures.

A U.S. Patent to Reifenhauser et al No . 3,664,796 discloses a manifoldarrangement for an extrusion assembly in which the manifold receives hotmelt plastic from an extruder screw and divides the material to supplytwo melt streams to a plurality of extrusion dies.

By the process and apparatus of the present invention, a valve, whichmay be in the form of a manifold, is directly connected with a singleextruder and divides the flow of hot plastic from the extruder into twostreams and passes at least one of the streams through a tortuous pathfor an even melt flow and, in certain cases, for additional heating. Thetwo flows of plastic material are then connected with a dual meltchamber dual slot die in which one melt chamber is heated to a highertemperature than the other, to supply plastic material to each chamberof the die in preselected proportions to effect the efficient bonding ofthe high temperature plastic material having good flow and adhesivequalities with the lower temperature material outside of the die.

It is also recognized that in order to increase the adhesive qualitiesof one of the plastic materials, it should be heated to a temperatureabove the oxidation temperature of the resin of the thermoplasticmaterial. The other plastic material may then be heated to a temperaturelower than the oxidation temperature of the resin of the thermoplasticmaterial and will have no odor since the resin has not oxidized. Inorder to eliminate odor of the thermoplastic material heated to thehigher temperature, the high and low temperature films are combined andthe high temperature material is laid on a substrate, cooperating withthe plastic material heated to the lower temperature and trapping thepolyethylene odor caused by oxidation of the resin of the thermoplasticmaterial.

An advantage of the present invention is the effectiveness ofeliminating the oxidized resin odor of a high melt thermoplasticmaterial by enveloping the oxidized resin between a low temperatureplastic film and a substrate.

A further advantage of the present invention is the effective reductionof resin odor of a thermoplastic film used to coat another thermoplasticfilm by extruding the two films at different temperatures and combiningthe films outside of the die and laying the thermoplastic materialhaving a resinous odor on a substrate.

A still further advantage of the invention is that two compatiblethermoplastic materials may be heated to different temperatures in asingle die, with one thermoplastic material passed through a tortuouspath and heated to a high enough temperature to bond with a secondthermoplastic material, and the two materials maintained at the requiredtemperature when passing through the die and extruded through individualslots of the die and combined outside of the die, and odor may beeffectively controlled by the high temperature film on a substrate.

A still further advantage of the invention is the simplicity andeffectiveness of reducing thermoplastic resin odor by the provision of aflow divider valve dividing a single flow of hot melt plastic from anextruder into at least two flows, one of which is heated to a highertemperature than the other, and connecting the flow divider valve with amulti-manifold multi-slot die, arranged to maintain the material in onemelt chamber at a higher temperature than that in the other and toaccommodate bonding of the two materials to each other and to asubstrate outside of the die.

Another advantage of the invention is the ability to control odor of athermoplastic material heated above the oxidation temperature of itsresin by the provision of a dual manifold, dual slot die, arranged toprovide two flows of extruded material at different temperatures and toenvelop the material heated to a high enough temperature to produce aresin odor, between the lower temperature material and a substrate, andthereby eliminate resin odor.

Other objects, features and advantages of the invention will be readilyapparent from the following description of preferred embodimentsthereof, taken in conjunction with the accompanying drawings, althoughvariations and modifications may be effected without departing from thespirit and scope of the novel concepts of the disclosure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view illustrating the steps of an odor controlprocess as carried out in accordance with certain principles of thepresent invention.

FIG. 2 is a transverse sectional view taken through a flow divider valveutilized to carry out the invention to supply two streams of hot meltplastic to the extrusion die.

FIG. 3 is a transverse sectional view taken substantially along lineIII--III of FIG. 2, and illustrating the flow divider of the flowdivider valve.

FIG. 4 is an end view of the flow divider valve with the adjustmentshaft and support shown in transverse section.

FIG. 5 is a partial fragmentary view in side elevation of a modifiedform in which the invention may be embodied in which one film is passedthrough a heat exchanger along a tortuous path and heated to its hightemperature while passing through this path; and

FIG. 6 is a sectional view taken through the heat exchanger and flowdivider valve shown in FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS OF INVENTION

In FIG. 1 of the drawings, we have diagrammatically shown the apparatusfor carrying out an extrusion coating and odor control system inaccordance with the principles of the present invention as including anextruder 11 which may be of the screw or worm feeder type and forces thehot plastic into and through an extruder valve 12 which may screen andmeter the plastic to a flow divider valve 13, dividing the flow andforcing the hot plastic through tortuous paths to provide an even meltrun to a plurality of melt chambers (not shown) in an extruder die 15.The die 15 is arranged to heat the plastic to different temperatures ineach melt chamber and extrude the plastic through extrusion nozzles, tobe combined outside of the die and laid on a substrate 16 as turningabout a pressure roll 17, biasing the substrate 16 to have a relativelyhigh temperature plastic film 18 combined with a lower temperatureplastic film 19 laid thereon under pressure and chilled by a chill roll20, as passing through the pressure nip between the pressure roll 17 andchill roll 20.

The extruder 11 may be a conventional form of extruder in which a screwor worm extrudes a plastic material, which may be a polyethylene, heatedin the extruder to an even flow temperature but below the oxidationtemperature of the resin, as for example, a temperature of 580° F. Theextruder 11 forces the material through the extruder valve 12 in whichthe melt flow is passed through a series of screens (not shown) andmetered by a suitable metering valve (not shown) through an outlet 21 ofthe valve to an inlet fitting 22 of the flow divider valve 13.

The extruder valve 12 may be like that shown and described in U.S. Pat.No. 3,307,217, dated Mar. 7, 1967, which meters the hot melt plasticthrough screening means (not shown) under the control of a hand wheel23. The extruder valve 12, therefore, need not herein be shown ordescribed further, since it forms no part of the present invention,except insofar as it forms a screening and metering means for the hotmelt plastic, and a means for supplying the screened and metered plasticto the inlet 22 of the flow divider valve 13.

The flow divider valve 13 is shown in particular in FIGS. 2, 3 and 4 ofthe drawings as including a valve body 25, shown as being in two parts,the parts of which are suitably secured together and sealed in asuitable manner. The adjacent body parts of the valve body 25 havealigned recessed portions 26 opening toward each other to define anopening and mounting for a center block 27 clamped between the bodyparts 25 and suitably sealed thereto. The center block 27 forms ineffect a "T" and has a threaded passageway 29 extending thereinto andterminating into a smaller diameter passageway 30, leading to a largerdiameter transverse passageway 31, opening at its opposite ends intoaligned passageways 32 and 33 in the body parts 25. The threadedpassageway 29 forms a threaded connection for the fitting 22 fitted tothe outlet 21 of the extruder valve 12 and suitably sealed thereto. Thefitting 22 has a flanged outer end portion 35 abutted by an adapter yoke36. The adapter yoke 36 may be drilled in a plurality of places toprovide holes 37 for studs 39 threaded in the outlet 21 of the extrudervalve 12. Nuts 40 threaded on the outer ends of the studs 39 are adaptedto draw the flange 35 into sealing engagement with said outlet and tothereby couple the fitting 22 and flow divider valve 13 to the outlet ofthe extruder valve 12. The nuts 40, drawing the yoke 36 and flange 35into tight engagement with the outlet 21 in cooperation with the studs39 and yoke 36, thus serve to rigidly connect said flow divider valve tothe outlet 21 of the extruder valve.

The center block 27 thus accommodates the discharge of hot melt plasticthrough opposite ends of said fitting under the control of a flowdivider 41. The flow divider 41 is shown as being generally cylindricalin form of an outside diameter having a sliding fit with the passageway31. As shown in FIGS. 2 and 3, the flow divider has oppositely slopingfaces 42 and 43 converging toward a peak 44 which may be close to thecenter line of the passageway 30, making allowance for an adjustment rod45, to divide the flow equally between the passageways 32 and 33.

The flow divider 41 is slidably moved along the passageway 31 by therectilinearly adjustable rod 45, welded or otherwise secured to thesloping face 43 of said valve and extending along the passageway 33outwardly of the body part 25, through a support sleeve 46 for saidshaft. Said support sleeve has an adapted flange 47 at the end thereofadjacent the body part 25, and retained to said body part as by machinescrews 48 extending through the adapter flange 47 and threaded in thebody part 25, as shown in FIG. 4. The support sleeve 46 also has aflange 49 at its outer end, recessed to receive a flange 50 of aninternally threaded adjustment nut 51, threaded on a threaded endportion 52 of the shaft 45 and externally threaded for a hand wheel 53.The hand wheel 53 is threaded on the outer end of the nut 51 and issecured thereto to turn said nut upon turning movement of said handwheel, as by one or more set screws 55.

The support sleeve 46 has a keyway 56 extending therealong and receivinga feather key 57, keyed to the shaft 45 and holding said shaft fromrotation during turning movement of the nut 51 and hand wheel 53 andaccommodating rectilinear movement of said shaft and adjustment of theflow divider to properly proportion the flow to the passageways 32 and33 in the body part 25. A hold-down ring 58 is bolted to the flange 49and engages the outer side of the flange 50 to hold said flange and thenut 51 from rectilinear movement upon adjustable movement of the shaft45. The hold-down ring 58 may be suitably bolted to the flange 49, as bybolts 58a limiting inward movement of said hold-down ring relative tothe flange 49 and preventing tightening of said hold-down ring againstthe flange 50 sufficient to retard rotation of said flanges.

The passageways 32 and 33 are shown as being elbow-like in form and openat right angles to the center line of the passageway 31 for dischargingthe hot melt plastic from the passageways 32 and 33 through right angledoff-set reducer passageways 59 and 60 in reducer adapters 61 and 62. Theoff-set reducers 61 and 62 may be secured to the bottoms of theindividual body parts 25 as by cap screws (FIG. 4). Adapters or couplers63 and 65 are shown as being threaded in the respective off-set reducerpassageways 59 and 60, and depending therefrom. The reducer adaptershave shouldered bottom portions as indicated by reference numeral 66,and forming stops for the shoulders of die adapter rings 67, adaptingthe reducer adapters to the inlet passageways of the extruder 15 andsecuring the adapters 63 and 65 to said extruder to supply athermoplastic mix to each melt chamber of the extruder die 15. Theadapters 63 and 65 may be encircled by adapter heaters 70 and 71,respectively. The adapter heaters 70 and 71 may be resistor heaters tomaintain the temperature of the plastic melt as extruded to the die at apreselected temperature range. The heaters may, if desired, supply theplastic melt to the extruder die 15 at different temperatures, toelevate the temperature of the plastic extruded through one adapterabove that extruded through the other. The heaters 70 and 71 need notnecessarily heat the adapters to different temperatures and the heatingof the material in the two melt chambers and keeping the hot meltmaterial to the desired temperature is attained by a high temperatureheater 72 diagrammatically shown as extending along one side of the bodyof the extruder die 15 and a lower temperature heater 73 extending alongthe opposite side of the body of the extruder.

Opposite ends of the body parts 25 may be closed by resistor heaters 75secured thereto as by cap screws 76. Thermocouples 77 may be inserted inthe reducer adapters and serve to control the temperatures of theheaters 70, 71 and 75 and the interior temperature of the flow dividervalve.

The respective reducer adapters 63 and 65 may each have a melt mixer 79therein forcing the plastic melt to travel along a tortuous path priorto discharge from said adapters into the extruder 15. The melt mixersmay be of a form known to those skilled in the art and providingpassageways between lands 80 of the mixers, and through said lands, andbeing arranged to force the mix to pass from one passageway to the otherthrough tortuous paths prior to discharge from the adapters, and tothereby effect a complete mix of the hot melt plastic and provide aneven flow of the hot melt plastic to and through the die. The meltmixers may be press-fitted, or otherwise secured to the adapters and maybe sealed to the die as by sealing rings 82 which may have sealingengagement with the body of the extruder die block. The adapter rings 67afford a means for securing the adapters 63 and 65 in communication withthe hot melt inlets (not shown) of the dual slot die 15, and may besecured to the body of said die to maintain the passageway leadingthrough one adapter in communication with one melt chamber of the dieand the passageway leading through the other adapter in communicationwith the other melt chamber of the die, as by machine or cap screws in asuitable manner, and no part of the present invention, so not hereinshown.

The dual melt chamber dual slot die may be of a type similar to thatshown and described in an application Ser. No. 316,863, filed by JamesJ. Melead on Dec. 20, 1972, U.S. Pat. No. 3,877,857, and no part of thepresent invention, so not herein shown or described further. Theextrusion die of application Ser. No. 316,863 is shown as an end feedrather than a top feed extrusion die. The feed, however, may be eitheran end feed or top feed die and in the present application, top feed ispreferable, since the die has only two melt chambers and two flows ofthermoplastic material are supplied to the die.

The extruder die 15 and heaters 72 and 73, extending along oppositesides of the die are so arranged as to maintain one melt chamber at atemperature in the range between 520° and 580° F. which is beneath theoxidation temperature of the thermoplastic material, and maintain theother melt chamber at a higher temperature, as for example, in the rangebetween 620° and 650° F. which is high enough to oxidize the resin ofthe thermoplastic material and provide good flow and adhesive qualitiesto the material, as combined with the film sheet extruded at the lowertemperature.

The heaters 72 and 73 are controlled by individual thermostats andthermocouples (not shown) which may be capable of setting the heaters todifferent temperatures and maintaining the heaters at these temperaturesas desired or required for good bonding qualities of the film 18 withthe film 19.

As described herein, the plastic materials extruded through the die 15may be the same material and may come from a common extruder and aredivided and supplied to the die 15 in separate melt streams at differenttemperatures . This enables the plastic material heated to the highertemperature above the oxidation temperature of its resin and thus givingoff an odor which can never be eliminated, to be bonded to the lowertemperature thermoplastic material, sealing one side of the hightemperature plastic material. The combined thermoplastic films may thenbe laid on a substrate extending along the high temperature side thereofand cooperating with the lower temperature plastic material tocompletely envelop the material heated to the higher temperature andcontain the odor to this material and thereby eliminate all odor of thebonded sheet. This also reduces deterioration and pin holes in thecompleted sheet by closing the pin holes by the low temperature film andsubstrate.

The thermoplastic material is usually a polyethylene material, but maybe a polypropylene or other plastic materials, such as modifiedpolyethylenes, ionomers and other polymers.

The substrate 16 coated by the films 18 and 19, may be paper which isdry when coated so as not to curl. The substrate may even be an extrudedplastic film, heated to the temperature of the plastic film 19 andextruded to cover the opposite side of the plastic film 18 from theplastic film 19. This may be supplied by a separate extruder die and theplastic film, while usually of the same material as the plastic films 18and 19, may be of a different material to not only contain the odor tothe high temperature plastic film, but also to provide a laminatedsheet.

Where the substrate is paper, it may be dry and of a suitable type notsubject to curling, as the high temperature film 18 is laid thereon, andin the end, resulting in a paper coated with plastic particularlysuitable for packaging purposes.

In the form of the invention illustrated in FIGS. 5 and 6, we utilizethe same extruder, metering valve and dual slot die as in the form ofthe invention illustrates in FIGS. 1 through 4. Like reference numerals,therefore, will be applied to the same parts in FIGS. 5 and 6 as areapplied in FIGS. 1 through 4.

In the modified form of the invention, a heat exchanger 85 forms a morecircuitous path for the high temperature stream than in the form of theinvention illustrated in FIGS. 1 through 4, to give a larger areaexposed to heat and a greater length of time for additional heat to soakinto the plastic in the high temperature flow stream. The heat exchanger85 is in the form of a block or body part secured to the bottom of theassociated body part 25 in the same manner the reducer adapter 61 issecured to the body part 25 in the form of the invention illustrated inFIGS. 1 through 4. The heat exchanger 85 depends from the associatedbody part 25 and extends to one side of said body part. Said heatexchanger 85 has a passageway 87 in communication with the passageway 32and turning at right angles to a looped passageway 88 having arectilinear flow portion leading ouwardly from said body part and thenturning inwardly to a parallel rectilinear outlet flow portion andterminating into a right angled downwardly extending dischargepassageway 89 having an adapter 90 threaded therein. The adapter 90 issimilar to the adapter 63 of FIG. 2 and has an adapter ring 91 on thelower end thereof adapting an adapter to an inlet passageway of theextruder die 15 and securing said adapter thereto. Resistor heaters 92extend along each side of the body part and in end-to-end relation alongeach side and are secured thereto as by machine screws 93 abuttingspring washers 95 and tightened against said spring washers until aportion of the spring in the washers is taken up. Terminals 96 areprovided at one end of the body part 86 to energize the resistor heatersat this end of the body part. Terminals 97 are provided at the oppositeends of the body part to independently energize the heaters at theadjacent end of the body part. A thermocouple 99 extends into the bodypart 85 along the rectilinear portion of the looped passageway 88 andserves to control the temperature of the adjacent resistor heaters 92 onopposite sides of the body part. A similar thermocouple 100 extends intothe parallel rectilinear portion of the looped passageway. The meltmixers 101 are placed in end-to-end relation with respect to each otherin the parallel rectilinear portions of the looped passageway 88 and maybe of a form known to the art so only described in sufficient detail torender our invention readily understandable. Each melt mixer has atapered end 103 facing the flow through the passageway and a wing-liketrailing end engaging the wall of the passageway and holding the meltmixer in position in the passageway. The melt mixers are furrowed alongthe leading ends thereof and have passageways extending along thetrailing ends thereof at right angles to the furrows extending along theleading ends and having communication with the furrows to provide acircuitous path for the plastic flow stream as passing along said meltmixers, in a manner similar to the melt mixer 79 in FIG. 2. The meltmixers 101 in the inlet rectilinear portion of the looped passageway 88are retained in position in said passageway by the thermocouple 99. Themelt mixers 101 in the parallel rectilinear portion of the loopedpassageway 88 in a like manner are retained in position by thethermocouple 100 leading into said looped passageway and abutting an endmelt mixer.

The melt mixers 101 thus provide a tortuous or circuitous path for theplastic stream as passing along the looped passageway 88 to the inlet ofthe extruder die 15 and attain a thorough mixing of the high temperatureplastic stream and provide a greater heat exchange area for the plasticstream and lengthen the time of passage along the heat exchanger fromthe form of the invention illustrated in FIGS. 1 through 4 to assure athoroughly mixed stream heated to the preselected high temperaturerequired to oxidize the resins of the thermoplastic material and thusbreak down the thermoplastic stream to give it good adhesive qualitiesto be bonded to the lower temperature plastic stream passing along theadapter 65 and melt mixer 79 into the low temperature side of theextruder die 15.

The extruder die 15 is like that diagrammatically shown in FIG. 1 andhas a high temperature heater extending along the side thereof connectedto the adapter 90 and a low temperature heater extending along the sidethereof connected with the adapter 65. The high temperature heater 72serves to merely maintain the temperature of the plastic stream as itpasses into the melt chamber of the extruder die 15 to be extrudedthrough an adjacent slot of the die in the form of a thin film. Theheater 73 may supply additional heat to the low temperature plasticstream where the heater 71 may not be sufficient to bring the plasticstream up to temperature, but in many cases, may serve to maintain thetemperature of the low temperature plastic stream sufficiently high toretain the flowability qualities of the plastic stream without breakingdown the plastic. While the same form of melt mixer is shown in theadapter 65 in FIG. 6 as in the same adapter shown in FIG. 4, it shouldbe understood that this melt mixer need not necessarily be used but thata melt mixer or a series of melt mixers like the melt mixers 101 may beplaced in said adapter in end-to-end relation with respect to eachother.

Except for the increased heating path along a heat exchanger 85 and meltmixers 101 in said heating path to give the plastic material more timefor additional heat to soak into the plastic and to afford a greaterheat exchange area for heating the plastic, the form of the inventionillustrated in FIGS. 5 and 6 is carried out like that illustrated anddescribed in connection with FIGS. 1 through 4 and there is no change inthe carrying out of the extruding and bonding process even though thehigh temperature plastic film is brought up to temperature beforeentering the extruder die.

The apparatus of both forms of the invention just described attains anextrusion coating process in the form of laminating a substrate withpolyethylene heated to a temperature high enough to break down theresins of the polyethylene and enclosing or enveloping the polyethylenesubject to odor by a polyethylene heated to a lower temperature, belowthe break-down temperature of its resin and, therefore, not subject toodor, in such a way that both the substrate and polyethylene coatingsentirely contain the odor in the polyethylene heated to a highertemperature and, therefore, provide a coated substrate particularlyuseful for packaging materials for foods and other products andarticles.

What is claimed is:
 1. An apparatus for combining and controlling theodor of multi-layer extrusion films, comprising:a single extruder fordelivering a thermoplastic melt stream, means dividing said melt streaminto first and second streams, first heating means to heat said firstone of said streams to a high enough temperature to oxidize the resin toattain good flow and adhesive characteristics, said first heating meansincluding mixing means to mix the resin to allow for uniform heatingthereof in said first heating means, second heating means to at leastmaintain the second streams at a lower temperature than the firststream, said temperature of said second stream being below the oxidationtemperature of the resin, die means disposed downstream of the first andsecond heating means having two side-by-side passages therein,, a thirdheating means associated with one of said passages and a fourth heatingmeans associated with the other of said passages, said third heatingmeans maintaining the first melt stream at said high temperature throughthe die and said fourth heating means maintaining the second melt streamat said lower temperature through the die, means for extruding thematerial so heated in the form of a film through the die in side-by-siderelation, and means for combining the two plastic materials with eachother and laying the adhesively heated material on a substrate andcoating the substrate under pressure.
 2. The apparatus of claim 1,wherein both films are polyethylene plastic materials, means areprovided for heating the enveloped film at a temperature in the order of620° F. and extruding the film at this temperature and means areprovided for heating the other film at a temperature in the order of580° F. and extruding the film at this temperature.
 3. The apparatus ofclaim 1, wherein the mixing means defines a circuitous and tortuouspath.
 4. The apparatus of claim 1, wherein said first heating meansheats the plastic flow stream to a high enough temperature to oxidizeits resin along a high temperature circuitous tortuous path to allow agreater area and time for additional heat to soak into the plastic flowstream in the higher temperature flow path, and further includes amixing means to maintain the plastic flow stream at this hightemperature and provide for uniform heating of the plastic stream. 5.The apparatus of claim 1, wherein the substrate is paper, means forcombining the two plastic films outside of the die as extruded, andpressure means adhesively laying the heated film on the substrate underpressure during combining of the two films.
 6. The apparatus of claim 5,wherein one flow stream of plastic material is heated to a temperaturein the range between 620° and 650° F. while the other flow stream ofplastic material is heated to a temperature in the range between 530°and 580° F.
 7. The apparatus of claim 1, wherein the substrate is paperand the two films are combined and laid on the substrate outside of thedie under pressure and cooling.
 8. The apparatus of claim 7, wherein theflow stream of plastic material heated to the higher temperature isheated to a temperature in the order of 650° F. and the flow stream ofplastic material heated to a lower temperature is heated to atemperature in the order of 580° F.